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New model/prototype

10-03-2006, 05:58 AM

Here are some pictures of my current project of making a fully mechanical (no batteries required) auto fire bb gun. This may be of interest because all parts are machined (using my mini mill or mini lathe) to some extent.

The picture was rotated sideways, the Algor (finite element analysis software) and Autodesk Inventor boxes were simply used because I keep them at the front of the bookshelf and they were the right size to prop things up. Actually, it seems appropriate as in a sense the project rests on those 2 bits of software. The 3d models and 2d CAD detail drawings were generated using Inventor while the frame that holds both my mini mill and lathe were structurally verified before being built by doing a finite element analysis to determine approximate maximum stress and deflections. I actually had subscriptions for both so I basically kept the box from the first versions and threw the rest (of the boxes) away after detaching the barcode & serial numbers. So all my software CD and updates are in one box each instead of about 50.

There is a 4000 count bb container and a 12g co2 cartridge for scale. The 12g cartridge was intended for the uzi/mac10 (box magazine attached thru the handgrip) submachine pistol but then I ran across a much larger 255g Brass Eagle refillable bottle. Since I had originally wanted a carbine size I decided to shelve the pistol design since the carbine has almost identical mechanism with main exception being it can have a larger, rugged box magazine without having a â€œfatâ€‌ feeling pistol grip. Of course the carbine shoots a lot longer (approximately 20x) before needing to recharge/replace the c02 power source. The larger 255g Brass Eagle refillable co2 bottle is obviously a lot bigger and you can see its simple and robust end fitting seal/connection which finalized my decision to go with it.

Since I donâ€™t have cnc (yet) the shells/ outer housings were made of wood, â€œchicken fenceâ€‌, plastic screen, cardboard and â€?bondoâ€™ automotive body putty. Hand shaped and mostly cosmetic these will be patterns for making the injection molded parts -at least for prototypes and early low volume production until I can get a cnc mill and make a more commercial quality (prettier and less variation from the 3d model) set of patterns. They are outer patterns, inner cores will of course be machined precisely and located with dowels in the molds. Again, the inner cores will be rather basic while once I get cnc capability I can make cores that reduce the amount of excess polymer material to make the part by making it more of a true shell rather than a block with a few bores and hollow boxes in it. I just painted them with dark green lacquer except for the stock cover which I broke while sanding. I neglected using screening just cardboard and bondo (over wood formers later removed) which doesnâ€™t tolerate too rough handling when its that thin. I was holding it near the middle and sanding away on the other end like it was 1/4â€‌ thick reinforced plastic instead of 1/16â€‌ bondo sandwiching 1/16â€‌ thick cardboard. The picture of the shells make them look worse than they are as they hadnâ€™t been finish sanded and polished yet and there was orange peel, bad lighting, and somewhat out of focus picture.

The 12â€‌ length sch40 pipe for the outer barrel is turned down to .75â€‌ od. Beautiful but it needs something to blue or otherwise surface treat so it doesnâ€™t rust. I really donâ€™t want to paint as that would remove the fine lathe tool marks which some might consider a blemish but which I prefer (on a gun barrelâ€™s outer surface) to a finely ground â€œperfectâ€‌ barrel finish. Next to the 12â€‌ outer barrel is an 8â€‌ inner barrel which is an alloy of aluminum/magnesium I think but it was scrounged from my model rc airplane supplies so not sure precisely what alloy. So it looks like my initial prototype will have only an 8â€‌ barrel tho Iâ€™m still thinking of 12â€‌ for the final product. Brass or bronze would be better inner barrel but none Iâ€™ve found have precisely the same id as this -which is ideal for bb. For production I intend to locate a supply for brass or bronze inner barrels but there may be some aluminum alloys that have good wear resistance and low coefficient of friction with steel.

The magazines are 30-40 round depending on spring used and one prototype is aluminum and a larger is acetal. The larger is simpler to make using only 2 half pieces (instead of 3 stacked) and has room for larger diameter spring. The left shows a close up of the acetal mag since the main picture is sadly lacking. The corners were nicely rounded using approx 1/16â€‌ - 1/8â€‌ r corner rounding/radiusing endmill. The magazine outer surface is very non slippery and secure grip since it was milled using a rough end mill. It would be nice if I could pattern and injection mold this as it takes hours to machine (without cnc) but I fear the surface texture would not transfer even to silicon or plaster-of-paris mold. Well, its already made and I intend the production version to use a 3.5â€‌ od approximately 300 round drum w/ helix feed magazine. The drum mag will definitely be molded so the box mag is likely only to see use initially and only in prototype testing (since its already built).

The intended design parameters are for a muzzle velocity of about 400 fps (at about 3-6 rounds/second) which with bbs should provide at least several 300 round magazines before changing/recharging the power source ( have to wait for tests and tuning before I can give any definite figures on muzzle velocity and endurance). This design is NOT intended for hunting or to kill anything, definitely not anything larger than sparrows or rabid chipmunks (although misuse could seriously or fatally injure people or pets â€“but then so could stumbling on the sidewalk). 400 fps gives a lot of paper target shredding power and should easily penetrate empty aluminum soda cans (a bb gun favorite target of mine). Yes, there are 22 caliber hunting pellet guns using a comparable air source shooting around 1000 fps to kill game up to raccoon size- BUT they can only shoot a dozen or so shots per canister. And even though 1000fps is about the same as a .22 caliber firearm, the pellet (which masses a lot more than a bb) is still a lot less massive than a .22 caliber bullet meaning its â€œstopping powerâ€‌ is a lot less. My interest here is in high rate of fire and have little current interest in designing anything that might be confused with a firearm (ballistically speaking) or that would require large 20 pound scuba tanks on the back. Mass production model cost estimated at approximately $50-$100 depending on features, manufacture methods and materials, and inclusion of brass eagle or equivalent refillable power cartridges ( those cost almost as much as the carbine itself).

This design would only require slight modifications to produce a paintball or softair versions although if I did that I might rearrange the magazine to point up (at an angle to clear the sights) and just use gravity feed although drum/helix mag may appeal more by not requiring it to be held upright to feed and fire rounds. Of course the bores would need to be changed as well as the tuning of the various springs. But still, no batteries required unless you want a laser sight of course.

Designed by degreed mechanical engineer, BSME

I donâ€™t give out my name because I once almost got fired for calling an idiot an idiot in an e-mail. Plus Iâ€™m a healthy 40 yrs old and certainly donâ€™t need to be put on a spam list for cheap Canadian viagra meds.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Comment

Sorry, I don't think peddling stuff is allowed here. I did mention a target cost of $50-$100 mass produced not to try and drum up customers but simply that any design you may consider even potential for future sale you need to set a target price which will eliminate alot of manufacturing methods and keep you from specifying in the prints to mill it from a block of titanium or something similar that would utterly bankrupt a commercial attempt.

Of course custom crafted, entirely cnc machined "works" products can be made (for astronomical price) and in effect my prototype is in that nature except I'm being cheap and trying to skip closer to the mass produced item using (home made)plastic injection molding with patterns easily made from wood, bondo, acetal, and/or machinable wax.

For pests I don't intend it to have alot more than 400fps but maybe tunable via spring & bolt change between 400-600 but that still is only good, like I said for sparrows and rabid chipmunks. Don't shoot a person with it, not even in self defense. I suspect it would make them much MORE likely to kill you than less.

I hope to have several limited edition hand crafted versions ready before Christmas to try to sell for enough to buy a cnc mill and quit my day job too. Ha, ha. Not likely, true. But its part of the American (and probably Canadian, British, Chinese, etc, etc) dream.

By the way, for the turned steel outer barrel does anyone have any suggestions for a good blueing compound or some similar surface treatment that really inhibits rust without changing the surface detail? I was originally thinking some kind of crude electroplating to give it a sort of stainless steel finish but may just use simple blueing.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Comment

That sounds like what I'm after. Of course for production an ugly plastic barrel will be likely be necessary to keep costs down but for my own I want it pretty even if only half of it is visible.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Comment

I just read up on it too (the Caswell kit) but I imagine they are all similar. A few points I believe are very important:

1. Nickel plating is very enviroment friendly- no toxic waste sludge produced like in the chrome plating tetravalent method. IE no hazardous waste dump in your backyard.

2. Nickel plating provides the same functionality as chrome plating, looks almost as pretty, and also very cheap even disregarding hazardous waste disposal of chrome plating.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Comment

Mechanical operation ok. I did mention that it was entirely mechanical which means no little electric motor or batteries necessary. I never actually used or disassembled a paintball gun so am not real familiar with the benefits of poppet. Um, any fully mechanical full auto or even semi auto single action would require "blowback" which is rather vague and self explanatory while not really explaining how my mechanism works. To clarify, my inspiration was the Crosman Walther ppk/s bb gun that works by what I term blowback (not a stupid revolver like most of em) and while not really a great deal similar in detail the concept is very similar. The Crosman ppk is a very fun bb pistol that I highly recommend despite its ballistic shortcommings compared to other c02 bb pistols due to the blowback having to move the realistic steel slide weighing nearly the same as a real 9mm firearm and that it has such a very short barrel. It does have a "kick" like a real .22-.32 caliber firearm auto pistol which is expending some of the power that could be propelling the bb.

Lets just say that my mechanism has more similarities with real firearms than with paintball or most bb guns. And I admit that I was thinking of and eventually used a mechanism similar in many respects to a real military rifle (but older than the m-16 and ak47). The Russian Drozd uses the tiny 12g c02 (plus it requires batteries) where my carbine uses 255g refillable c02 so no comparison there at all tho the Drozd probably looks prettier. Aside from having a Bachelor of Science degree in Mechanical Engineering (BSME) I was also in the Army for 4 years active duty the last 2 years or so as the arms room nco (sergeant e-5).

Its possible my mechanism is very similar to some pnuematic air hammers (although I have never disassembled one so maybe not).

I'm checking out your other links right now, I love seeing stuff like that. Frankly, I wouldn't consider buying the Drozd even if they were only $50 but if you got something better... I can never have too many bb guns, especially since the big companys like Daisy and Crosman mostly just built the same crap bb guns that were around when I was a kid (probably when my grandpa was a kid too).

Hmm, your pistol looks like a pump to me. Also like a precision target type. I think the world has more than enough single shot bb guns, I want to shred paper. Maybe its just me, being in the Army all that time and I only once got to shoot an m16 on full auto. Yeah, shot the m-60 but its a "crew served" weapon so not the same. When in the weapons platoon I was always assigned as the 60 or m203 gunner when what I wanted was the SAW.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Hermann von Helmholtz (1821-1894)

Comment

Ok, I've decided to show the carbine "blowback" mechanism here just for the record since I do not plan to patent it, because it is rather prosaic and besides very similar at least in concept to the WW2 m1 carbine "short-stroke piston" mechanism. "in the Williams system the gas port leads to a small hollow block beneath the barrel, inside which is a flat headed piston with a stem barely half an inch long protruding through the back of the block...When the gas behind the bullet goes through the port in this design it drives the tiny piston back very forcefully, since the piston weighs no more than couple of ounces. The system is light, simple, and easy to manufacture, which makes it all the more surprising that few other designs have ever adopted it." (Handguns and Rifles: The Finest Weapons from around the World", Ian Hogg. Similar in concept, but not ever having an m1 carbine to disassemble I cannot say how similar in detail. Heres a picture with some other parts not shown. This is "for the record" in case someone tries to patent my design which I likely won't ever patent. The tiny stem is what transfers the mechanical impulse to throw the bolt back. The radial holes simply vent the back side of the short stroke piston and can tune down (ie, increase resistance, air spring type damping in the event the transferred force is far larger than desired causing excess wear and fatigue) the fairly great deal of force from a given pressure charge (due to its surface area being alot larger than the projectile bore).

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Hermann von Helmholtz (1821-1894)

Comment

Ah, the light came on about the poppet valve question. The answer is that I will use as efficient a valve I can make or buy. For example a "poppet" valve is usually more efficient than a ball check valve although generally more difficult to make but the difference in effeciency can vary and overlap. So, yes if I can buy poppet valves cheap instead of the ones I am currently making (non cnc, not really high precision) and hand lapping. Of course a butterfly or gate valve may provide less resistance but then are generally more problematic getting a true consistent seal. I don't want the majority of the c02 leaking out when it hasn't even been used after all.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

Um, can you provide a specific example of any of your complaints listed above? For example, just because most existing bb and paint ball guns are practically clonal copies of each other doesn't mean that they are well designed. I am arrogant, in that I do not take well to vague philosophical suggestions. But mostly I was just speaking of personal preference when saying things like, "I think the world has more than enough single shot bb guns.."

Your point about heavy on CAD plans is good tho, but I always prefer too much detail to insufficient. It does tend to make me get sidetracked on almost purely cosmetic items (like the shell which is only to enclose and protect the innards and could easily look more like near scale outlines of the mp-44 or ak-47, and plating the steel barrel which could be turned out of pvc or other plastic ). Just because you may know the name of more obscure widgets than I do does not mean you comprehend their operating principles. I may be wrong here but for example a "poppet" valve I seem to recall the air pressure is always seeking to pop the valve open which requires spring to keep closed, and though an automotive type valve also has a spring the air tends to close the valve or at least not force it open. Which is better and for what application? Well, poppet valves are no longer used in internal combustion engines while they seem to have found favor in bb and paintball guns likely due to simple ignorance.

By the way, I think you should stick to poetry and not argue engineering principles with degreed engineers.

â€œIt was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌